JPH0654704B2 - Manufacturing method of self-regulating surface heating element - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial application] The present invention relates to a self-temperature controlling planar heating element having positive characteristics (hereinafter abbreviated as planar heating element).

[Prior Art] The conductivity of a substance is determined by the number of charge carriers in the substance and the mobility of the carriers. In the case of carbon, since the carriers are conduction band electrons, the number of carriers is Aexp (-W / k) according to the number of electrons in the conduction band, and thus Boltzmann's rule.
T), where A is a constant, W is the band gap between the valence band and the conduction band, k is the Boltzmann constant, T is the absolute temperature, while the mobility is also generally Aexp (-W / kT). It is represented by. Here, A is a constant and W is the activation energy of hopping. Therefore, the temperature change of the electric conductivity (δ) can be generally expressed by δ = δ ₀ exp (−ΔE / kT). However, there are some substances that follow the above formula at a certain temperature or lower, but exhibit a resistance value much higher than that calculated by the above formula at a certain temperature or higher. This substance is called a positive characteristic.

Conventionally, as an inorganic substance having a positive characteristic, a substance obtained by adding a trace amount of rare earth element to barium titanate has been used. On the other hand, among organic substances, carbon-paraffin-polyethylene type is known as one having a large positive characteristic, but this composition has poor compatibility, and there are problems in the mixing method and changes in characteristics over time. In addition to this, carbon-nylon compositions have been used, but the positive characteristics are not so great.

In recent years, as a composition for improving such a problem, a composition composed of an organic compound containing a plurality of alkylene oxides in a molecule as a unit structure and carbon is given, and the composition is sealed with an electrode in an insulator. Proposals for heating elements have been made. Further, JP-A-50-150039 and JP-A-51-48843 propose a planar heating element using a mixture of carbon fine particles and a heat-vulcanizable silicone rubber.

[Problems to be Solved by the Invention] However, in the conventional composition, carbon-paraffin-polyethylene and carbon-nylon have the above-mentioned disadvantages, and polyethylene, nylon, etc. are not coated with a suitable solvent. Since a mold cannot be formed and a planar heating element must be formed by high-temperature processing by extrusion molding or calendar molding, equipment costs and processing costs are high, and the shape is limited to a specific shape.

On the other hand, the alkylene oxide-carbon composition gives a large positive characteristic and gives a sheet-like heating element that operates stably, but it has a drawback in heat resistance, and in particular under high voltage, it becomes a kind of short-circuited sheet-like heating. Therefore, there is a problem that it is likely to generate linear heat and lack safety.

Furthermore, these conventional sheet heating elements set a positive characteristic region according to the mixing ratio of carbon to be mixed, that is,
It was manufactured by changing the mixing ratio of carbon and determining the mixing ratio by judging from energization time, temperature rise and resistance value.

Therefore, in a sheet heating element having a small electrical resistance value and a high temperature positive characteristic and a large amount of mixed carbon, a compatibility problem between the composition and carbon occurs, and in the setting of the positive characteristic region, This involved complicated work of changing the mixing ratio of carbon one by one.

Furthermore, in a planar heating element in which carbon fine pieces and thermosetting silicone rubber are mixed, it is necessary to change the mixing ratio when setting the temperature at which the electric resistance value changes abruptly. There is a problem that it cannot be performed easily and the material cannot be reduced.

The present invention is to solve the above problems, a mixture of carbon in a room temperature curable or low temperature curable silicone rubber composition, a heat-sensitive electrical resistance composition sheet heat-cured at a temperature of room temperature or higher, It was found that a sheet heating element having a self-temperature control function with a large positive characteristic according to heating conditions can be obtained without changing the mixing ratio of carbon, and it can be manufactured at low cost and has excellent heat resistance. I came to see this completion here, knowing that I could get a safe one.

That is, it is an object of the present invention to provide a novel self-temperature controlling planar heating element having such a self-temperature controlling function by using carbon fine particles in a silicone rubber composition.

[Means for Solving the Problems] A method for producing a self-temperature regulating planar heating element of the present invention for achieving the above object comprises silicon rubber and carbon fine pieces,
In the method for producing a self-temperature controlling planar heating element in which a heat-sensitive composition sheet having a property of abrupt change in electric resistance with respect to temperature change is sealed with an insulator together with a pair of electrodes, the silicone rubber has a property of curing at room temperature. A room temperature curable type silicone rubber having at least 3 or more silicon atom-bonded hydrolyzable groups in one molecule and having a viscosity at 25 ° C. of 20.
Those containing 0 to 2000 P of organopolysiloxane, or having at least two silanol groups or two silicon atom-bonded hydrolyzable groups in one molecule at 25 ° C.
Containing an organopolysiloxane having a viscosity of 200 to 2000 P and an organosilicon compound having at least an average of two silicon-bonded hydrolyzable groups in one molecule, or rapidly curable by heating at a relatively body temperature A low-temperature curable silicone rubber having properties, wherein 100 parts by weight of an organopolysiloxane having at least two alkenyl groups bonded to a silicon atom in one molecule and having a viscosity at 25 ° C. of 200 to 2000 P is used as a crosslinking agent. Organopolysiloxane having an average of more than 2 hydrogen atoms bonded to atoms in one molecule is mixed at a compounding ratio of 0.1 to 10 parts by weight, and a platinum-based catalyst as a curing agent is added to 0.00
0001 to 0.1 part by weight is added, and a silicon rubber composition obtained by mixing the carbon fine pieces in a compounding ratio of less than 30 parts by weight with respect to 100 parts by weight of the silicone rubber is applied to a non-conductive sheet or After being impregnated and supported, it is heated to a predetermined temperature of room temperature or more and cured to form the heat-sensitive composition sheet.

[Operation] In the RTV or LTV silicone rubber of the present invention, the organopolysiloxane present in the molecule thereof plays an important role together with the carbon fiber pieces, and when it is heat-cured, it has a positive characteristic. In the setting of the region (2), even if the mixing ratio of carbon is not changed, an arbitrary self-temperature controllable function can be obtained depending on the condition of the heat curing temperature, and a unique extremely stable and large positive characteristic is exhibited.

[Example] FIG. 2 (a) is a plan view showing an example of the planar heating element of the present invention, and FIG. 2 (b) is a sectional view taken along line XX of FIG. 2 (a). . In this example, two rectangular non-conductive covering sheets 2 and 2 using the heat-sensitive electric resistance composition sheet 1 as an insulator
At the time of sealing between the sheets, the following composition was applied to a glass base, and the sheet was cured and peeled off at room temperature and 50 ° C., and the copper foil electrodes 3 were provided on both edges of the sheet.

The composition contains 90% by weight of condensation reaction type organopolysiloxane (KE1402, manufactured by Shin-Etsu Sirincon Co., Ltd.) as an RTV silicone rubber (a) component described below and 10 parts by weight of a curing agent (Cat1402, manufactured by Shin-Etsu Silicon Co., Ltd.) as a (B) component. % Was used, and 9 parts by weight of acetylene carbon was mixed with 100 parts by weight of the composition.

Silicone rubber was applied to the non-conductive coating sheets 2 and 2 and cured to form a planar heating element having a length of 5 cm and a width of 7 cm. Its thickness is less than 2 mm.

3 and 4 are graphs showing the positive characteristics when the sheet heating element was energized from a 100 V power source.

In the same manner as in the above-mentioned example, the heat-sensitive electric resistance composition sheet 1 was added with an addition reaction type organopolysiloxane (Shin-Etsu Sirincon, Ltd.) as an LTV silicone rubber (A) component described later.
A composition was used in which 100 parts by weight of KE1300) and 10 parts by weight of a catalyst (Cat1300, manufactured by Shin-Etsu Silicon Co., Ltd.), which was a combination of the organopolyhydrogensiloxane as the component (B) and the platinum-based catalyst as the component (C), were added.

In addition, 9 parts by weight of acetylene carbon was used, and the heat curing treatment was performed at 80 ° C and 100 ° C.

Graphs of this positive characteristic are shown in FIG. 3 and FIG.

The temperature-current graph shown by the broken line in FIG. 4 is the temperature-current characteristic graph of the sheet heating element obtained by curing carbon fine pieces at 12 parts by weight at room temperature. Has a very large rush current and is inferior in stability over time.

Incidentally, when mixing the carbon fine pieces in the above examples, the mixing ratio which is compatible and does not phase separate is usually less than 30 parts by weight, preferably 100 parts by weight of the silicone rubber composition, in the silicone rubber composition. Is less than 20 parts by weight, but a sheet obtained by heating and curing a mixture of an amount equal to or less than this mixing ratio at room temperature or higher has a desired positive surface property as judged from the energization time, temperature rise, and change in resistance value. Use as a heating element. For example, for 100 parts by weight of RTV silicone rubber,
Fig. 1 shows the time and temperature changes when electricity is applied to a sheet-like heating element obtained by heat-treating a sheet of heat-sensitive electric resistance composition containing 9 parts by weight of acetylene carbon at room temperature, 50 ° C, 80 ° C, and 100 ° C. Like

Heat curing treatment is about 50 ℃ at room temperature, about 80 ℃ at 50 ℃,
The temperature reaches about 100 ℃ at 100 ℃ and about 130 ℃ at 100 ℃, and the equilibrium temperature is reached. That is, in FIG. 1, it is found that the heat curing temperature and the temperature at which the electric resistance value changes abruptly. Therefore, if a constant 9 parts by weight of acetylene carbon is mixed with the RTV silicone rubber composition and the heating and curing temperature is changed, the heater and the thermostat do not have to change the mixing amount of the acetylene carbon and have a self-temperature control function. A sheet heating element can be obtained.

That is, the sheet heating element of the present invention is obtained by applying a mixture of carbon fine particles to the above silicone rubber composition to a non-conductive sheet such as plastic film, paper, glass, ceramic or thin woven cloth, nonwoven cloth, sponge sheet. Alternatively, it is impregnated and supported and heat-cured to obtain a heat-sensitive electric resistance composition sheet, which is sealed with two front and back non-conductive coating sheets, and conductive wires are attached at predetermined intervals inside the sheet, and the whole sheet is formed. Is a sheet-shaped sheet heating element.

As described above, the silicone rubber and the carbon fine particles are made into a room temperature curable type having a property of curing the sirconcon rubber at room temperature or a low temperature curable type having a property of rapidly curing by heating at a relatively low temperature of 50 ° C. to 150 ° C. It is found that the target temperature at which the electric resistance value is suddenly changed can be obtained by the heat curing temperature of these compositions even if the compounding ratio of is constant.

The room temperature curable and low temperature curable silicone rubber compositions used in the present invention are classified into a one-pack type and a two-pack type in terms of form, and condensation reaction type organopolysiloxanes which are roughly classified according to the curing mechanism. Although there are addition reaction type organopolysiloxane compositions, any of them can be used in the present invention.

Such an organopolysiloxane composition can be used at room temperature
It hardens into a rubber at a temperature in the range of 150 ° C and is used as an electrical insulating material, molding material, sealing material, sealing material, etc.

Here, the condensation reaction type organopolysiloxane composition is
For example, as the component (a), an organopolysiloxane having at least two silanol groups or silicon atom-bonded hydrolyzable groups in one molecule, and as the component (b), at least two silicon atom-bonded hydrolysates on average. The organosilicon compound having a functional group is contained in an amount sufficient for the composition to be RTV or LTV.

The component (a) is a main component of the condensation reaction type organopolysiloxane composition, and its molecular shape is linear.
It may be branched or reticulated, preferably linear. At least two silanol groups or silicon atom-bonded hydrolyzable groups are required in one molecule because they are necessary for curing, and may be present at either or both of the terminal end and side chains of the organopolysiloxane. From the viewpoint of physical properties after curing, it is preferably present at the end of the molecular chain. Examples of the organic group bonded to the silicon atom of the organopolysiloxane include an alkyl group such as a methyl group, an ethyl group, a propyl group and an n-octyl group, an alkenyl group such as a vinyl group and an aryl group, a phenyl group and a naphthyl group. Aryl group, cyclohexyl group, cycloalkyl group such as cycloheptyl group, 3-chloropropyl group, halogenated alkyl group such as 3,3,3-trifluoroalkyl group, 2-phenylethyl group, 2-phenylpropyl group, etc. There is an aralkyl group, and these organic groups may be used alone or in combination of two or three in one molecule. Among these, it is general that only a methyl group or a mixture of a methyl group and another organic group is present. It is usually preferable that the viscosity of this component at 25 ° C. be in the range of 200 to 2000 p. A silanol group is usually used as a group involved in the crosslinking reaction contained in this component, but a silicon atom-bonded hydrolyzable group can also be used. The silicon atom-bonded hydrolyzable group is a functional group capable of hydrolyzing to generate a silal group, and any conventionally known functional group can be applied to this functional group. Specifically, for example, an alkoxy group, an amino group, an amido group, an aminoxy group oxime group,
There are alkenoxy groups and the like.

The organosilicon compound having at least two silicon atom-bonded hydrolyzable groups in one molecule of the component (b) is
(A) It is necessary for the silanol group in the component or the silicon atom-bonded hydrolyzable group to undergo a condensation reaction with the silanol group generated by hydrolysis to hang the rubber-like structure, in other words, for the composition to cure. It is an ingredient.

When the component (a) has two silanol groups or silicon atom-bonded hydrolyzable groups in one molecule,
Since the component (b) requires an average of more than 2 silicon atom-bonded hydrolyzable groups on average, the component (b) contains organosilicon having 3 or more silicon atom-bonded hydrolyzable groups in one molecule. The presence of compound molecules is required. When the component (a) has three or more silanol groups or silicon atom-bonded hydrolyzable groups in one molecule, the component (b) component 1
It suffices that there be an average of two silicon atom-bonded hydrolyzable groups in the molecule. In addition, in the (b) component, 3 in one molecule
Organosilicon compounds having one or more silicon-bonded hydrolyzable groups may be present.

(A) The total number of silanol groups or silicon atom-bonded hydrolyzable groups in one molecule of component (b) and the total number of silicon atom-bonded hydrolyzable groups in one molecule of component (b) is 4 or more. Is not preferable.

The hydrolyzable group in the component (b) may be any functional group capable of hydrolyzing to form a silanol group. As an example, the hydrolyzable group of the component (a) is applied.

The other valence of the silicon atom of the component (b) that is not bonded to the hydrolyzable group is satisfied by the carbon atom of the unsubstituted or substituted hydrocarbon group or the oxygen atom of the siloxane bond. As this hydrocarbon group, a monovalent hydrocarbon group is usually used, but a divalent or higher valent hydrocarbon group can also be used. The monovalent non-hydrocarbon group includes an alkyl group, an alkenyl group and an aryl group, and the monovalent substituted hydrocarbon group includes a halogenated hydrocarbon group, an amino substituted hydrocarbon group, an epoxy substituted hydrocarbon group and a mercapto substituted group. There are hydrocarbon groups, ester-substituted hydrocarbon groups, ether-substituted hydrocarbon groups and the like. Further, two or more silicon atoms may be bonded by a divalent or higher valent hydrocarbon. Silane, which is a monomer, is the most common component (b).

Examples of such a component (b) include alkoxy group-containing silicon compounds such as tetraethyl silicate, tetra (normalpyropyl) silicate, and ethyl polysilicate, and 2 to 4 N, N-diethylaminoxy groups in one molecule. It is also possible to use a combination of plural kinds of methylcyclosiloxanes each having. Further, for obtaining a one-pack type RTV composition, that is, a composition that can be stored in an uncured state in a closed container for a long period of time and hardens when exposed to the air, for example, methyltriacetoxysilane or vinyltriacetate is used. Acetoxysilane, ethyltriacetoxysilane and the like can also be used. Furthermore, methyltri (cyclohexylamino) silane, methyltri (dimethylketoxime) silane, vinyltri (methylethylketoxime) silane,
Methyltri (isopropenoxy) silane, vinyltri (isopropenoxy) silane, methyltri (N-ethylacetamido) silane, etc. can also be used.

The amount of the component (b) added is an amount sufficient to cure the composition, and varies depending on the number of functional groups of the component (a) and the component (b), the type of functional group, the molecular weight, and the like. When the component (a) has three or more silicon atom-bonded hydrolyzable groups in one molecule, the component (b) does not need to be added, but the component (b) is other than the above. If, then (b)
Addition of ingredients is necessary. In that case, it is preferable to add the component (b) so that the silanol group or the silicon atom-bonded hydrolyzable group of the component (a) has the same equivalent amount or more of the silicon atom-bonded hydrolyzable group.

Next, the addition reaction type organopolysiloxane composition may be, for example, (A) an organopolysiloxane having at least two alkenyl groups bonded to a silicon atom in one molecule, and (B) a silicon atom bonded to the silicon atom. It is a composition for curing an organopolysiloxane having an average of more than two hydrogen atoms in one molecule by using a platinum catalyst of component (C).

The organopolysiloxane as the component (A) may have either a linear or branched skeleton, and in order to obtain a rubber-like structure by curing, an alkenyl group bonded to a silicon atom is
It is necessary to have at least two in the molecule. Examples of the other organic group bonded to the silicon atom include the organic group of the component (a) of the condensation reaction type organopolysiloxane. Further, a hydroxyl group may be present at the molecular end or the like. The viscosity of this component is also preferably in the range of 200 to 2000 p.

The organopolysiloxane as the component (B) is a cross-linking agent for the organopolysiloxane as the component (A), and may have any chain-like, branched or network-like siloxane skeleton. In order to form, it is necessary to have an average of more than 2 hydrogen atoms bonded to a silicon atom in one molecule.

As the organic group bonded to the silicon atom, those similar to the organopolysiloxane of the component (A) are used.

The addition amount of the component (B) is preferably 0.1 to 10 parts by weight with respect to 100 parts by weight of the organopolysiloxane of the component (A).

The platinum-based catalyst as the component (C) is a catalyst that promotes the hydrosilylation reaction between the components (A) and (B), and is, for example, chloroplatinic acid, chloroplatinic acid and an olefin, or a silane containing an alkenyl group. A compound, a polysiloxane containing an alkenyl group, a complex obtained from cyclopropane or alcohol, a platinum-organophosphine complex, a platinum-organophosphite complex and the like can be used.

The amount of the platinum-based catalyst added to the component (C) is determined by the curability during working time, but 0.000001 to 0.1 part by weight, preferably 0.00005 to 0.01 part by weight, relative to 100 parts by weight of the organopolysiloxane of the component (A). It is a range of parts.

The composition of the component (a) and the component (b) of the condensation reaction type organopolysiloxane used in the present invention or the composition of the component (A) and the component (B) and the component (C) of the addition reaction type organopolysiloxane. Other than that, if necessary,
For example, curing accelerator, heat resistance improver, flame retardant, antifungal agent,
Adhesion aids and the like may be added appropriately, and solvents such as toluene and hexane may be used for the purpose of adjusting the viscosity. Further, other organopolysiloxane can be used in combination.

The sheet heating element obtained by the production method of the present invention is suitable as a floor heating device for buildings, a snow melting device, a heating carpet, a heating mat for agricultural and livestock such as brooding and raising seedlings, glass, a substrate for preventing dew condensation such as a mirror. It is something.

EFFECTS OF THE INVENTION The present invention heats a mixed composition containing room temperature curable silicone rubber or low temperature curable silicone rubber and carbon fine particles while keeping the compounding ratio constant. By curing, it becomes possible to obtain a target temperature that causes the electrical resistance to change abruptly according to the heating and curing temperature, and the temperature setting at which the electrical resistance changes abruptly can be set by the heating and curing temperature instead of the mixing ratio of the carbon fine pieces. Therefore, the temperature can be easily set, and the sheet heating element can be manufactured at low cost because coating and impregnation can be performed at a temperature of about room temperature without performing high temperature processing.

[Brief description of drawings]

FIG. 1 is a graph showing the relationship between the energization time and the temperature of a heat-treated mixed composition of RTV silicone rubber and acetylene carbon, and FIG. 2 (a) shows an example of the planar heating element of the present invention. A plan view and FIG. 2B are sectional views taken along line XX of FIG. FIG. 3 is a graph showing composition temperature and electric resistance characteristics of the heat-treated electric resistance composition sheet, and FIG. 4 is a graph showing composition exothermic temperature and electric current characteristics of the heat-sensitive electric resistance composition sheet. is there. 1 ... Thermosensitive electrical resistance composition sheet 2 ... Non-conductive coating sheet 3 ... Electrode

Claims (1)

[Claims] 1. A self-temperature regulating sheet heating element comprising a heat-sensitive composition sheet made of silicon rubber and carbon fine particles, the sheet having a property of suddenly changing electric resistance with respect to temperature changes, and a pair of electrodes sealed with an insulator. In the method, the silicone rubber is a room temperature curable silicone rubber having a property of curing at room temperature, and has at least 3 or more silicon atom-bonded hydrolyzable groups in one molecule at 25 ° C.
Containing organopolysiloxane having a viscosity of 200 to 2000 P, or at least 2 per molecule.
Organopolysiloxane having 1 silanol group or 2 silicon-bonded hydrolyzable groups and having a viscosity at 25 ° C. of 200 to 2000 P and at least 2 per molecule in average.
A silicon-bonded alkenyl compound containing an organic silicon compound having a silicon-bonded hydrolyzable group, or a low-temperature curable silicone rubber having a property of rapidly curing when heated at a relatively low temperature. Having at least two groups in one molecule and having a viscosity at 25 ° C. of 200 to 20
In 100 parts by weight of organopolysiloxane of 00P, an organopolysiloxane having a number of hydrogen atoms bonded to a silicon atom as a cross-linking agent in an average of more than 2 hydrogen atoms in one molecule of 0.
1 to 10 parts by weight is mixed, and 0.000001 to 0.1 parts by weight of a platinum catalyst is added as a curing material, and 30 parts by weight of the carbon fine pieces are added to 100 parts by weight of this silicone rubber. After coating or impregnating the non-conductive sheet with a silicone rubber composition mixed at a compounding ratio of less than that, the above heat-sensitive composition sheet is formed by heating to a predetermined temperature of room temperature or higher and curing treatment. A method of manufacturing a self-regulating surface heating element, characterized by: